JP5625690B2 - Valve for engine - Google Patents

Description

  The technology disclosed herein relates to an engine valve that opens and closes a port that opens to a combustion chamber of an engine, and more particularly to a heat insulating structure thereof.

  In the case of a metal product exposed to a high-temperature gas such as an engine component, a heat insulating layer is formed on the surface of the metal base material in order to suppress heat transfer from the high-temperature gas. For example, Patent Document 1 describes a valve in which a heat insulating structure is added to the surface of an umbrella portion from the viewpoint of increasing the degree of freedom in selecting a constituent material of the valve. In this document, as a specific example of the heat insulating structure, a structure made of a heat insulating material such as ceramic oxide is formed on the surface of the umbrella portion of the exhaust valve using means such as thermal spraying (Configuration Example 1). In addition, a configuration (configuration example 2) is described in which a thin heat shield plate with a reinforcing rib made of a heat resistant material such as heat resistant steel is attached to the valve head surface of the intake valve.

JP 2003-307105 A

  In order to improve the fuel efficiency of automobiles, weight reduction of the vehicle body, improvement of engine thermal efficiency, reduction of mechanical resistance, reduction of electric load, recovery and use of exhaust energy, and the like are being attempted. Of these, regarding the thermal efficiency of the engine, it is theoretically known that the higher the geometric compression ratio and the higher the excess air ratio of the working gas (the higher the specific heat ratio), the higher the thermal efficiency. It has been. However, in actuality, the larger the compression ratio and the larger the excess air ratio, the greater the cooling loss (energy lost to the outside as heat). Improvements in thermal efficiency will peak.

  That is, the cooling loss depends on the heat transfer rate from the working gas to the engine combustion chamber wall, its heat transfer area, and the temperature difference between the gas temperature and the wall temperature. Among them, the heat transfer coefficient is a function of gas pressure and temperature. Therefore, when the gas pressure and temperature increase due to an increase in the compression ratio and excess air ratio, the heat transfer rate increases and the cooling loss increases. Moreover, since the temperature difference between the wall temperature and the gas temperature also increases, this also increases the cooling loss. For this reason, for example, an ultra-high compression ratio of 20 or more is also a high expansion ratio, and although it is effective in reducing exhaust loss, it cannot be realized due to the cooling loss. Currently.

  On the other hand, it is conceivable to improve engine efficiency (improve fuel efficiency) by collecting exhaust energy instead of greatly increasing the compression ratio. However, in this case as well, when the cooling loss is large, the exhaust energy is reduced accordingly. Therefore, as in the case of increasing the compression ratio, it is important to reduce the cooling loss.

  In order to reduce the cooling loss, it is necessary to insulate the combustion chamber. As a part of the heat insulation structure of the combustion chamber, it is considered to use the heat insulation structure of the intake / exhaust valve described in Patent Document 1. It is done. However, in the configuration example of Patent Document 1, in order to increase the degree of freedom in selecting a valve material by reducing the amount of heat input to the umbrella portion, for example, in Configuration Example 1, the surface of the umbrella portion is about 0.1 to 2.0 mm. It is a configuration provided with a thin heat insulating film, and as described above, sufficient heat insulating property that can contribute to the reduction of cooling loss cannot be realized, and the heat insulating film is directly attached to the entire surface of the valve. In the configuration, due to the difference in coefficient of thermal expansion between the base metal of the valve and the coating, the coating may be peeled off or damaged, resulting in low reliability.

  On the other hand, in the configuration example 2 of Patent Document 1, since the space between the valve head surface and the heat shield plate becomes hollow, the heat insulation performance can be higher than that in the configuration example 1, but the thin heat shield plate with the reinforcing rib is used as the valve. In a structure that is fixed to the head surface, it is difficult to stably maintain the hollow structure against high combustion pressure and temperature in the combustion chamber, and there is a problem in durability and reliability of the heat insulating structure. .

  The technology disclosed herein provides a heat insulating structure for a valve that can ensure high heat insulating performance, high durability, and reliability, and can be used to reduce cooling loss of an engine.

  The technology disclosed herein is directed to an engine valve that includes a valve body including a shaft portion and an umbrella portion, and that opens and closes a port opened in the combustion chamber of the engine. The valve head faces the combustion chamber in the umbrella portion. The surface is formed with a recess recessed from the valve head surface at least in a portion excluding the central portion and the outer peripheral edge of the surface, and the engine valve includes air in the recess. The porous material filled in the concave portion and at least the central portion and the outer peripheral edge portion of the valve head surface are bonded to each other to cover the valve head surface including the concave portion and to conduct heat more than the valve body. And a film having a low rate.

  According to this configuration, the heat insulating layer is formed on the valve head surface side of the engine valve by the concave portion formed in the valve head surface, the porous material filled therein, and the coating covering the valve head surface. Since the recessed portion filled with the porous material can contain air therein, a high air heat insulation effect can be secured, and the specific heat capacity (volume specific heat) can be made smaller than that of the valve body. And since the membrane | film | coat which coat | covers a valve head surface covers the recessed part with which the porous material was filled, while being able to hold | maintain a porous material stably, even when a high combustion pressure acts, for example, it can prevent damage to a porous material .

  On the other hand, since the coating itself can be secured to at least the central portion and the outer peripheral edge of the valve head surface, a sufficient bonding area can be secured, so that the bonding strength and bonding stability of the coating can be obtained. The film may be further bonded to the porous material in the recess. In addition, the film is only bonded to the central part and the outer peripheral edge of the valve head surface of the valve body, and is not attached to the entire valve head surface over a wide range. It can be advantageous in improving durability and reliability by suppressing peeling and breakage due to a difference in thermal expansion coefficient between the constituent material of the main body and the coating.

An intermediate portion is provided between a central portion and an outer peripheral edge portion of the valve head surface, and the concave portion is formed in a portion excluding the central portion, the outer peripheral edge portion, and the intermediate portion, and the film is you are joined at least the central portion of the valve head surface, each of the outer peripheral portion and the intermediate portion. By doing so, the bonding area of the film can be further expanded, so that the bonding strength and bonding stability of the film can be further increased.

  The intermediate portion is annular, and the first concave portion between the central portion and the intermediate portion and the second concave portion between the intermediate portion and the outer peripheral edge portion are provided concentrically. Each of the first recess and the second recess may be filled with a porous material, and the porosity of the first recess and the porosity of the second recess may be different from each other.

  Preferably, the porosity of the second concave portion on the outer peripheral side is made higher than the porosity of the first concave portion on the inner peripheral side. The umbrella portion of the bulb has a relatively thin outer peripheral portion as compared with the inner peripheral side, but high thermal insulation performance can be ensured in the thin outer peripheral portion. Note that the porosity of the first recess and the porosity of the second recess may be the same.

  The said porous material is good also as being comprised with the nonwoven fabric made from a heat-resistant metal. Non-woven fabric made of refractory metal is advantageous for long-term stabilization of heat insulation performance due to high shape stability in the recess, ensuring high strength against external force, etc., and durability and reliability of the heat insulation layer It becomes advantageous for improvement.

  The heat-resistant metal nonwoven fabric may have an oxidized surface. By filling the non-woven fabric into the recess and covering it with a film, the non-woven fabric can contact the inner surface of the recess and also contact the film. In other words, heat can be conducted through the contact area, but oxidizing the surface of the nonwoven fabric is advantageous in reducing the heat conductivity and suppressing the heat conduction through the contact area and increasing the heat insulation effect of the combustion chamber. obtain.

The film may contain ZrO ₂ as a main component. A film composed mainly of ZrO ₂ has a relatively low thermal conductivity, a thermal conductivity lower than that of the valve body, and a volumetric specific heat also lower than that of the valve body. As a result, the heat insulating performance of the valve can be further improved.

  As described above, according to the above-described engine valve, the concave portion formed on the valve head surface is filled with the porous material, and the valve head surface including the concave portion is joined to at least the central portion and the outer peripheral edge portion. Since the heat insulating layer is formed by covering with the coated film, high durability and reliability of the heat insulating layer can be obtained while ensuring high heat insulating performance. As a result, it contributes to reducing the cooling loss of the engine, which is advantageous in directly increasing the thermal efficiency of the engine or indirectly increasing the thermal efficiency of the engine through the recovery of exhaust energy.

It is sectional drawing which shows the engine structure which concerns on embodiment. It is a graph which shows the relationship between the geometric compression ratio (epsilon) of an engine from which specifications differ, and the illustration thermal efficiency. It is a graph which shows the relationship between the excess air ratio (lambda) of the engine from which a specification differs, and illustration thermal efficiency. (A) The longitudinal cross-sectional view which expands and shows the umbrella part of a valve | bulb, (b) It is a bb sectional view taken on the line. FIG. 5 is an enlarged vertical cross-sectional view of the structure of the valve different from that of FIG. 4, (a) a cross-sectional view taken along line bb.

  Hereinafter, the form of the valve for engines is explained based on a drawing. The following description of preferred embodiments is merely exemplary in nature. In this embodiment, an intake valve and an exhaust valve having a heat insulating structure are applied to the engine shown in FIG.

<Engine features>
In FIG. 1, 2 is a cylinder block, 3 is a cylinder head, 41 is an intake valve for opening and closing the intake port 5 of the cylinder head 3, 42 is an exhaust valve for opening and closing the exhaust port 7, and 8 is a fuel injection valve. The combustion chamber of the engine is formed by the top surface of the piston 1, the cylinder block 2, the cylinder head 3, and the front surface of the umbrella portion of the intake and exhaust valves 41 and 42 (the surface facing the combustion chamber, which is called the valve head surface). The A cavity 9 is formed on the top surface of the piston 1. The illustration of the spark plug is omitted.

  This engine is a lean burn engine that has a geometric compression ratio ε = 20 to 50 and is operated at an excess air ratio λ = 2.5 to 6.0 at least in a partial load region. Therefore, as described above, unless the cooling loss of the engine is significantly reduced, that is, the heat insulation of the engine is not increased, the desired thermal efficiency corresponding to the compression ratio ε and the excess air ratio λ is obtained. Can't get. This point will be described based on the indicated thermal efficiency by model calculation. That is, when the compression ratio ε was increased, a model calculation was performed to determine how the indicated thermal efficiency is affected by whether or not the combustion chamber has a heat insulating structure and by the magnitude of the excess air ratio λ.

  FIG. 2 shows the result. In the figure, “without heat insulation” means a conventional engine that does not employ a heat insulation structure in the combustion chamber, and “with heat insulation” means that the heat insulation rate of the combustion chamber is 50% higher than that of the conventional engine without “heat insulation”. % Means an engine that is higher. “200 kPa” and “500 kPa” represent the magnitude of the engine load.

  First, in the case of “no heat insulation 200 kPa λ = 1”, the illustrated thermal efficiency increases as the compression ratio ε increases. However, even if the compression ratio ε = 50 is exceeded, the illustrated thermal efficiency does not greatly improve, and the compression ratio ε Since the theoretical efficiency at = 50 is about 80%, the indicated thermal efficiency of the engine is considerably low. Most of this difference is cooling loss and exhaust loss.

  In the case of “without heat insulation 200 kPa λ = 2”, the specific heat ratio decreases due to an increase in the excess air ratio, so that the illustrated thermal efficiency is high, but it is still low in terms of theoretical efficiency. Looking at “without heat insulation 200 kPa λ = 4” and “without heat insulation 200 kPa λ = 6”, when the compression ratio ε exceeds 15 or 25, the indicated thermal efficiency decreases as the compression ratio ε increases. This is because the excess air ratio λ is large (the air density of the air-fuel mixture is high), so when the compression ratio is high, the gas pressure during combustion becomes very high, and the heat transfer coefficient as a function of the gas pressure and temperature is high. This is because the cooling loss increases. That is, the cooling loss becomes larger than the increase in thermal efficiency due to the increase in excess air ratio λ (increase in specific heat ratio).

  On the other hand, in the case of “with heat insulation 200 kPa λ = 2.5”, the indicated thermal efficiency increases as the compression ratio ε increases. In the case of “with heat insulation 200 kPa λ = 6” in which the excess air ratio λ is increased, when the compression ratio ε exceeds 40, the illustrated thermal efficiency slightly decreases, but the illustrated thermal efficiency is very high at the compression ratio ε = 20-50. It is a value. Even in the case of “with heat insulation 500 kPa λ = 2.5” in which the engine load is increased, the indicated thermal efficiency is high at the compression ratio ε = 20-50.

  FIG. 3 is a graph showing the relationship between the excess air ratio λ and the indicated thermal efficiency. In the case of “no heat insulation 200 kPa ε = 15”, the illustrated thermal efficiency peaks near the excess air ratio λ = 4.5, and the illustrated thermal efficiency decreases as the excess air ratio λ increases. On the other hand, in the case of “with heat insulation 200 kPa ε = 40”, the illustrated thermal efficiency peaks in the vicinity of the excess air ratio λ = 6.0. This is because the compression ratio ε is high and the cooling loss is suppressed by heat insulation.

  In the case of the lean burn engine, it operates at an excess air ratio λ = 2.5 or more at least in the partial load region, which is advantageous for suppressing NOx generation. As the compression ratio ε increases, the combustion temperature increases, but the excess air ratio λ is controlled to increase as the engine load increases, thereby suppressing NOx generation so that the maximum combustion temperature does not exceed 1800K. Can do.

  Although not shown, an intercooler for cooling the intake air is provided in the intake system of the engine. As a result, the in-cylinder gas temperature at the start of compression is lowered, the increase in gas pressure and temperature during combustion is suppressed, and this is advantageous in reducing cooling loss (improving the indicated thermal efficiency).

<Insulation structure>
In the following, heat insulation for reducing the cooling loss necessary for increasing the indicated thermal efficiency in the engine operated at the ultra-high compression ratio ε = 20 to 50 and the high excess air ratio λ = 2.5 to 6.0. The structure will be described.

FIG. 4 shows a reference example of the heat insulating structure of the intake or exhaust valves 41 and 42. In FIG. 4 (and FIG. 5 described later), the valve shape is exaggerated for easy understanding of the structure. Hereinafter, the intake valve 41 and the exhaust valve 42 are collectively referred to simply as valves. This valve includes a valve body 6 including an umbrella portion 61 that opens and closes intake or exhaust ports 5 and 7, and a shaft portion 62 that is continuous with the umbrella portion 61.

  The valve body 6 is made of heat resistant steel or cast iron, for example. As described above, this engine has reduced the exhaust loss as well as the cooling loss, so the exhaust gas temperature is relatively low. For this reason, it is also possible to use a material (for example, an aluminum alloy or the like) that could not be used conventionally or was difficult to use for the exhaust valve 42 in particular.

  The valve body 6 includes a heat insulating layer 63 on the valve head surface 611 side that forms the combustion chamber of the engine. The heat insulation layer 63 includes a recess 612 formed in the valve head surface 611, a porous material 64 in the recess 612, and a coating 65 that covers the entire surface of the valve head surface 611 including the recess 612.

  The recess 612 is formed to be recessed from the valve head surface 611 in a donut shape excluding the central portion and the outer peripheral edge of the circular valve head surface 611. The depth of the recess 612 may be set as appropriate as long as the umbrella portion 61 of the valve body 6 can ensure the necessary rigidity. The deeper the depth, the thicker the heat insulating layer 63 becomes. It becomes advantageous in raising. In addition, the width of the recess 612 (the width in the radial direction) may be set as appropriate within a range in which the bonding area of the film 65 can be sufficiently secured, as will be described later. Since the substantial area is enlarged, it is advantageous in improving the heat insulation performance.

  The recess 612 is filled with a porous material 64. The porous material 64 may be made of a non-woven fabric made of a heat-resistant metal such as stainless steel.

  As a specific example of the metal nonwoven fabric, a NASRON filter (trade name) manufactured by Nippon Seisen Co., Ltd. can be exemplified. That is, it is a filter made of SUS304, SUS316 or SUS316L made of short stainless steel fiber, long stainless steel fiber, stainless steel powder, or stainless steel wire mesh with a porosity of about 25 to 80%, and is filled with the recess 612. It can be used as the material 64.

  As another specific example, a laminated metal nonwoven fabric filter (trade name) manufactured by Semitec Co., Ltd., which is formed by laminating a reinforcing metal mesh or a protective wire mesh on a metal nonwoven fabric, can be exemplified. In this case, handling properties can be improved.

  Further, the porous material 64 may be constituted by a metal fabric formed in a three-dimensional manner using, for example, a heat-resistant metal thread (for example, Akihisa Higuchi, four others, “Development of a three-dimensional structured fabric using metal fibers”, 2004, Tokyo Metropolitan Industrial Technology Research Institute Research Report No. 7).

  By filling the concave portion 612 with the porous material 64, air is contained in the concave portion 612, so that the thermal conductivity is relatively lowered and the volume specific heat is also relatively reduced. As a result, the thermal conductivity of the concave portion 612 filled with the porous material 64 becomes lower than the thermal conductivity of the valve body 6, and the volume specific heat also becomes smaller than the volume specific heat of the valve body 6.

  The surface of the porous material 64 made of a metallic nonwoven fabric or the like may be oxidized in the atmosphere at 1010 ° C. to 1150 ° C. and 0.5 hr to 1 hr. Alternatively, a surface oxide film forming method for forming a thick oxide film by a method using ozone gas may be used. For example, a stainless steel member is housed in a processing chamber and evacuated by a vacuum pump, and then high-concentration ozone gas generated by an ozone generator is introduced from an ozone gas lead-out path and wet oxygen gas through a water storage device is introduced from a supply path. By doing so, wet ozone gas having an ozone concentration of 15 vol% or more may be used, and stainless steel may be treated at a predetermined temperature (60 ° C.) by heating with a heater to form an oxide film on the surface. The porous material 64 filled in the recess 612 can come into contact with the inner wall of the recess 612 and the coating 65, but the oxide formed on the surface has low thermal conductivity, so that heat conduction through the contact portion is suppressed and heat insulation is performed. This is advantageous in suppressing a decrease in the heat insulation performance of the layer 63.

  As the porous material 64, Tokai carbon glassy carbon microspheres (high-purity carbon having an amorphous structure and excellent stability in a vacuum of 3000 ° C. and in air of 500 ° C.) are used as a filter. It is also possible to use what is molded into

The film 65 can employ a metal oxide such as ZrO ₂ as its material. For example, when Y ₂ O ₃ stabilized ZrO ₂ (YSZ) is used as the coating material, the thermal conductivity of the coating 65 is 1.44 W / (m · K), and its volume specific heat is 0.46 kJ / (kg · K). Thus, the thermal conductivity can be lower than that of the valve body 6 and the volume specific heat can be reduced. The metal oxide film 65 can be formed on the valve head surface 611 by, for example, plasma spraying. In this case, the central part or the outer peripheral edge of the valve head surface 611 where the recess 612 is not formed is a film. The film 65 can be firmly bonded to the valve head surface 611 as a bonding allowance of 65, and the film 65 is also bonded to the porous material 64 in the recess 612. It can contribute to stabilization of the holding | maintenance of the porous material 64 in the recessed part 612 with conversion.

  A valve having such a heat insulating layer 63 can be obtained by the following method. That is, the porous material 64 is filled into the recess 612 formed in the valve head surface 611 of the valve body 6. Next, a coating 65 is formed by plasma spraying a coating material on the valve head surface 611.

  According to the heat insulating structure of this valve, since the recess 612 filled with the porous material 64 contains air, a high air heat insulating effect can be obtained. As a result, the amount of energy generated by the combustion of the fuel is taken to the outside as heat through the valve body 6 (cooling loss is reduced).

  In addition, when a metal nonwoven fabric is used as the porous material 64 and filled in the recess 612, the metal nonwoven fabric can exhibit high shape stability in the recess 612, so that the heat insulation performance is stable over a long period of time. This is advantageous for maintaining the pressure and the strength of the valve including the heat insulating layer 63 is increased, which is advantageous for improving durability and reliability. In addition, oxidizing the surface of the metallic nonwoven fabric is advantageous in improving heat insulation performance by suppressing heat conduction through the contact portion between the porous material 64 and the inner wall of the recess 612 and the coating 65.

  The film 65 prevents the penetration of the fuel into the recess 612 and the intrusion of carbon, and prevents the porous material 64 from being damaged by the external force or the like, or the porous material 64 from being detached or separated. Since the film 65 is directly bonded to the central portion and the outer peripheral edge portion of the valve head surface 611, sufficient bonding strength and bonding durability can be ensured. On the other hand, the coating 65 is only bonded to the central portion and the outer peripheral edge of the valve head surface 611 with respect to the valve body 6, and is not attached to the entire valve head surface 611. This can be advantageous in improving durability and reliability by suppressing peeling and breakage due to a difference in thermal expansion coefficient between the constituent material of the main body 6 and the film 65. In particular, forming the coating 65 by thermal spraying on the valve head surface 611 causes a part of the coating material to enter the voids in the outer surface of the porous material 64 composed of a metallic nonwoven fabric or the like in the recess 612. Since the porous material 64 made of a metal nonwoven fabric and the like is advantageous for holding and stabilizing the porous material 64 and can be somewhat deformed, it is possible to suppress peeling and damage of the coating film 65 due to the difference in thermal expansion coefficient described above. This is advantageous in improving the strength and durability of the film 65.

  As a result, it is possible to stably maintain a hollow structure using the porous material 64 over a long period of time, and as a heat insulating structure of the valve, high heat insulating performance and high durability and reliability are ensured. Is done.

As the coating material, for example, adopting a material having a low thermal conductivity and a small volume specific heat, such as Y ₂ O ₃ stabilized ZrO ₂ , is advantageous in ensuring heat insulation. In particular, when the volume specific heat of the film 65 is small, coupled with the small volume specific heat in the recess 612 containing air, the valve surface temperature rises rapidly as the combustion chamber temperature rises due to fuel combustion. At the same time, the temperature rapidly decreases as the combustion chamber temperature decreases. Therefore, the difference between the gas temperature of the combustion chamber and the surface temperature of the valve is not increased, and the cooling loss is reduced.

  The heat insulating structure of the valve may be configured as shown in FIG. 5, for example. In the following description, the description of the same structure as that of the valve shown in FIG. 4 may be omitted.

  In this configuration example, the first concave portion 613 on the inner peripheral side is formed in a portion excluding the central portion of the circular valve head surface 611, the outer peripheral edge portion, and the intermediate portion between the central portion and the outer peripheral edge portion. Two recesses, the second recess 614 on the outer peripheral side, are formed. That is, the intermediate portion is formed in an annular shape between the center portion and the outer peripheral edge portion, and thereby, the first recess portion 613 that is recessed in a donut shape between the center portion and the intermediate portion, and the intermediate portion, A second recess 614 that is also recessed in a donut shape is concentrically formed between the outer peripheral edges. Here, the width of the intermediate portion (the width in the radial direction) is appropriately set within a range in which the area of the concave portion including the first and second concave portions 613 and 614 is too small and the substantial area of the heat insulating layer 63 is not reduced. You only have to set it.

  The first concave portion 613 and the second concave portion 614 are each filled with a porous material 64, and so as to cover the valve head surface 611 including the first and second concave portions 613 and 614 filled with the porous material 64, The film 65 is formed by spraying, for example.

  In this configuration example, the intermediate portion of the valve head surface 611 can function as a joining margin of the coating 65 together with the central portion and the outer peripheral edge, so that the bonding area between the valve head surface 611 and the coating 65 is enlarged correspondingly. Will do. This is advantageous in improving the bonding strength and bonding durability of the film 65.

  In addition, from the viewpoint of increasing the bonding area of the film 65, the intermediate portion is not limited to being formed in an annular shape. The intermediate portion extending in the direction may be equally arranged with respect to the center of the bulb. In this case, the concave portion between the central portion and the outer peripheral edge portion is divided into a plurality in the circumferential direction by the intermediate portion.

  Further, the porosity of the first recess 613 and the porosity of the second recess 614 filled with the porous material 64 may be set to the same porosity by filling the same type of porous material 64, for example. Yes, but you can make them different. In particular, the porosity of the second recess 614 on the outer peripheral side of the valve umbrella 61 may be higher than the porosity of the first recess 613 on the inner peripheral side. This is because the umbrella portion 61 of the valve is thinner on the outer peripheral side and it is desirable to improve the heat insulating performance on the outer peripheral side.

  Further, in particular, the exhaust valve 42 is provided with a heat insulating structure similar to the above-described heat insulating structure on the valve head surface side on the valve face surface (the rear surface of the umbrella portion) opposite to the valve head surface in the umbrella portion. Also good.

  The valve provided with the heat insulating layer 63 disclosed herein is not limited to the application to the ultra-high compression ratio engine shown in FIG. 1, and may be applied to other engines.

41 Intake valve 42 Exhaust valve 5 Intake port 6 Valve body 61 Umbrella portion 611 Valve head surface 612 Recess 613 First recess 614 Second recess 62 Shaft 64 Porous material 65 Film 7 Exhaust port

Claims (5)

An engine valve having a valve body including a shaft portion and an umbrella portion, and opening and closing a port opened to a combustion chamber of the engine,
Wherein the valve head surface facing the combustion chamber in the valve head, a portion excluding an intermediate portion between these and the center portion and the peripheral edge portion of this said surface, said a recess which is recessed from the valve head surface formed And
A porous material filled in the recess so that the recess contains air;
A film having a thermal conductivity lower than that of the valve main body, covering the valve head surface including the concave portion by bonding to at least the central portion , the outer peripheral edge portion, and the intermediate portion of the valve head surface. Engine valve equipped. The engine valve according to claim 1 ,
The intermediate portion is annular, and the first concave portion between the central portion and the intermediate portion and the second concave portion between the intermediate portion and the outer peripheral edge portion are provided concentrically.
Each of the first recess and the second recess is filled with the porous material,
An engine valve in which the porosity of the first recess and the porosity of the second recess are different from each other. The engine valve according to claim 1 or 2 ,
The porous material is a valve for an engine configured by a nonwoven fabric made of a heat-resistant metal. The engine valve according to claim 3 ,
The heat-resistant metal nonwoven fabric is an engine valve whose surface is oxidized. The engine valve according to any one of claims 1 to 4 , wherein:
The coating is an engine valve mainly composed of ZrO ₂ .

Images